A carbon fiber bundle is in the form in which plural carbon single fibers containing carbon as a main component (the component contained in the largest portion) are combined together. When a carbon-fiber-reinforced thermoplastic resin is produced using this carbon fiber bundle as a reinforcing material for a thermoplastic resin, the carbon fiber bundle is used, for example, in the form of chops cut to a length of 3 to 15 mm, or in the form of a continuous fiber.
In a case in which a pellet are produced by kneading chops of a carbon fiber bundle and a thermoplastic resin, it is preferable that the carbon fiber bundle is quantitatively supplied to an extruder; however, in order to do so, morphological stability of the carbon fiber bundle is important.
Furthermore, in a case in which a sheet material is produced by mixing or weaving carbon fiber bundles and impregnating the mixture or woven fabric with a thermoplastic resin, or a long fiber pellet is produced, the carbon fiber bundles are usually supplied to the production process in the form of continuous fiber; however, the carbon fiber bundles are prone to have fluffs generated therein and are prone to loosen, and handling thereof is difficult. Meanwhile, in the case of using carbon fiber bundles in the form of a woven fabric, weaving performance of the carbon fiber bundles, woven fabric handleability after weaving, and the like also constitute important characteristics.
Due to the reasons described above, carbon fiber bundles converged by a sizing treatment for the purpose of enhancing handleability of the carbon fiber bundles or the properties of a material having carbon fiber bundles incorporated therein, have been traditionally used. Regarding this sizing treatment, generally, use is made of a method of applying a sizing agent having compatibility with thermoplastic resins that are used as matrix resins, to the surface of a carbon fiber bundle in an amount of, for example, about 0.2% by mass to 5% by mass with respect to the carbon fiber bundles.
For this thermoplastic resin, a polycarbonate resin, a nylon resin, a polyester resin, and the like are frequently used; however, in recent years, investigations have been made on the use of polyolefin-based resins from the viewpoints of recyclability and economic efficiency. Among them, polypropylene resins in particular are resins that are attracting more attention.
However, polyolefin-based resins usually do not have polar groups in the molecular chain, and tend to have very low interfacial adhesiveness to carbon fibers or glass fibers. Thus, many of them do not sufficiently manifest an effect of enhancing the mechanical characteristics as reinforcing materials.
For this reason, Patent Document 1 discloses a method of improving the interfacial adhesiveness to a polyolefin-based resin as a matrix resin, by subjecting carbon fibers, glass fibers and the like to a sizing treatment with a sizing agent containing an acid-modified polypropylene as an essential component.
Furthermore, Patent Document 2 describes a carbon fiber bundle to which a self-emulsifying polypropylene-based resin dispersion liquid that can be emulsified without using a surfactant, has been applied.
Moreover, Patent Document 3 describes a carbon fiber bundle in which a composition containing an acid-modified polyolefin and a glycol ether-based compound is adhered to the surface as a sizing agent.